This invention relates to thermal ink-jet (TIJ) printers, and more particularly to improvements in the pens used therein.
TIJ printers typically include a TIJ pen which includes a reservoir of ink coupled to the TIJ printhead. One type of pen includes a polymer foam disposed within the print reservoir so that the capillary action of the foam will prevent ink from leaking or drooling from the print-head. In such a foam-pen, an air-vented delivery system is provided wherein air enters the reservoir via a separate vent opening to replace ink which is dispensed from the reservoir through the printhead.
A different type of TIJ printer has an ink reservoir which is ordinarily maintained under a sub-atmospheric or negative pressure so that ink will not leak or drool from the printhead. Various types of ink reservoirs may be used including refillable ink reservoir cartridges which are mounted on the moveable printer carriage, throwaway replaceable cartridges which are mounted on the printer carriage, and remote or offboard ink reservoirs from which ink is brought to the printhead on the printer carriage by tubing.
A collapsible ink reservoir for an inkjet printer is disclosed in U.S. Pat. No. 4,422,084, issued Dec. 20, 1983, to Saito. Negative pressure is maintained in a polypropylene ink bag by various types of springs which bias the bag walls apart from each other. The springs may be mounted inside of or externally of the ink bag, but the spring pressure regulator construction does not result in substantially complete emptying of the ink bag and the bag itself is not carried on a printer carriage.
Another ink reservoir which achieves constant negative back pressure through an external spring or an elastomeric bladder is disclosed in U.S. Pat. No. 4,509,062, issued Apr. 2, 1985.
Large format ink-jet printer/plotters such as the DESIGNJET series sold by Hewlett-Packard Company offer substantial improvements in speed over the conventional X-Y vector plotter. Ink-jet printer/plotters typically include a plurality of print cartridges, each having a print head with an array of nozzles. The cartridges are mounted in a carriage which is moved across the page in successive swaths. Each ink-jet print head has heater circuits which when activated cause ink to be ejected from associated nozzles. As the cartridge is positioned over a given location, a jet of ink is ejected from the nozzle to provide a pixel of ink at a desired location. The mosaic of pixels thus created provides a desired composite image.
Recently, full color ink-jet printer/plotters have been developed which comprise a plurality of ink-jet cartridges of diverse colors. A typical color ink-jet printer/plotter has four ink-jet print cartridges, one for black ink (K), and three for color inks, magenta (M), cyan (C) and yellow (Y). The colors from the three color cartridges are mixed to obtain a full spectrum of color. The cartridges are typically mounted in stalls within an assembly which is mounted on the carriage of the printer/plotter. The carriage assembly positions the ink-jet cartridges and typically holds the circuitry required for interface to the heater circuits in the ink-jet cartridges.
Large scale printer/plotters have been developed which use cartridges with internal spring-bag reservoirs. Because of the volume of ink used in creating many plots, as well as the heavy usage to which the devices are put, the user must intervene to replace cartridges whose internal reservoirs have been depleted of ink. This can lead to expensive waste if a large scale plot is commenced, but must be discarded because one or more of the cartridges runs out of ink. The print media on which such plots are made is typically relatively expensive. Moreover, time is lost in commencing a large plot only to have to discard the plot because one of the cartridges runs out of ink before the plot is finished.
Thus there is a need in the art for systems and techniques for providing an increased supply of ink in printer/plotters employing spring-bag cartridges.
An ink-jet printer/plotter for ink-jet printing onto a print media is described, and comprises an ink-jet cartridge including an ink-jet print head and a closed spring-bag primary ink reservoir in fluid communication with the print head for holding an internal supply of liquid ink under negative pressure. The reservoir including a movable side wall and an internal spring for biasing the side wall against collapsing as ink is withdrawn from the reservoir and ejected from the print head onto a print medium during printing operations. The printer/plotter includes a frame and a print media advancing mechanism for advancing a print medium along a medium path in a media advance direction to a print area. A cartridge carriage holds the cartridge in a registered position, and a cartridge carriage drive mechanism moves the cartridge carriage relative to the frame along a carriage axis for printing a swath.
In accordance with the invention, an auxiliary ink reservoir is secured relative to the frame for holding an auxiliary supply of liquid ink. A connection tube runs between the primary reservoir and the auxiliary reservoir for providing a closed fluid path between the primary and auxiliary reservoirs. The printer/plotter includes means for positioning the auxiliary reservoir at a height position relative to the spring bag internal reservoir so as not to destroy the back pressure. Preferably, the height position of the auxiliary reservoir is below a height at which the print head is disposed while the cartridge is secured in the carriage for printing operation.
The auxiliary reservoir holds a large quantity of liquid ink to result in little variation in back pressure as ink is consumed. In a preferred embodiment, the auxiliary reservoir is a flat bag with relative large depth and width dimensions.
In accordance with another aspect of the invention, the auxiliary reservoir is supported by a spring-biased platform whose height varies as the weight of the auxiliary reservoir changes. As ink is withdrawn from the auxiliary reservoir to replenish the spring-bag reservoir, the reservoir weight decreases, and the platform and reservoir rise. This maintains a constant pressure and elevation head in the ink replenishment system.